Series gap device for lightning arresters



March 22, 1938. F. B. JOHNSON 2,112,097

SERIES GAP DEVICE FOR LIGHTNING ARRESTERS Filed NOV. 21, 1935 Pad/Um-Feafed 5/7/5077 Carb/de 3 WITNESSES; INVENTOR Mad/M fiea w/CK 5 Ja/mson.

m. fi nce, WW

ATTORNEY and third, after the surge-voltage has r Patented Mar. 22, 1938 UNITED STATES PATENT OFFICE SERIES GAP DEVICE FOR LIGHTNIVG ARRESTERS of Pennsylvania Application November 21, 1935, Serial No. 50,854

20 Claims.

My invention relates to protective discharge gaps, and it has particular relation to series-gap devices for lightning arresters. A lightning arrester has the property of changing from substantially an insulator, or at least from a very high resistance, to a fairly good conductor of electricity .in response to a predetermined ovenvoltage, and of returning to its initial state, or at least reducing the discharge-current to a relatively small value, upon restoration of mined normal voltage conditions.

The function of the series-gap device to my present invention applies is threefold: under normal conditions it keeps voltage appearing across the arrester element; second, when a surge of predetermined over-voltage applied, the series gap breaks down, allowing the passage of surge-current through the appeared, the series gap interrupts the re 1 4 or so-called power-follow, current flowing th the arrester, which is the aforesaid relative small value of discharge-current which flow in the arrester after the restoration 0:: mal voltage-conditions. Accordingly, the se gap device which would afford the greatest do of protection to the electrical circuit or conduct to which the combined series gap and arrestapplied would be a gap which would consist' have the lowest possible breakdown-voltage a surge is applied to it and which would still oonsistently have a sufficiently high 60-cycle, or normal-frequency, breakdown to prevent brealzdown on the application of the normal linevoltage. In addition, the series-gap device must have adequate arc-interrupting or quenching ability.

Prior to my present invention, it has been com mon to utilize one or more series gaps having electrodes of brass or similar materials, in connection with lightning arresters. These gaps have adequate quenching or so-called non arcing properties, but they have an undesirably high impulse-ratio, or ratio of surge-voltage breakdown to Gil-cycle breakdown; and their surge-breakdown voltage has been inconsistent, making it difficult to predict the operation of the gap under various conditions.

Heretofore, any efforts made to reduce the impulse-breakdown of a gap have involved the difficulty of obtaining adequate arc-quenching properties, because a gap-electrode material which will break down at relatively low voltage will, in general, also tenaciously hold onto the are after the arc has once formed, thus having poor use desirable properties of such lowlo-real wn gap-electrode substances, while still set .g required quenching ability of the series-gap device such as that which has been ally in use in connection with lightning to my present invention. 1' accompllsh this by causing the low-breakdown. substance to be u arc quenehing of this comb nation is occur according to the ealidown, high esistance will first be iated, "erial,

or .lal, tl'neie hat a concentrated arc-dis or are finally carried substantially only lot es stance electrode-niember. This 1e substantially instansly, or i =rnely short period of time, c voltage of t e c which terminates on the ll be lower e voltage necessary maintain the" -resistance electrode ma series-gap device has ir properties as if the lown material not been present. r tne foregoing and other objects in view, my invention consists in the combinations, structures and methods hereinafter described and. claimed and illustrated in the accompanying drawing, wherein Figure l is a plan view of a series-gap device in accordance with my invention, and

Fig. 2 is a cross-sectional view thereof, with a diagrammatic representation of electrical circuits and apparatus illustrating the application and use ofv my inve tion in connection with a lightning arrester for providing an excess-voltage protective device for an electrical circuit or conductor.

As shown in the drawing, my series-gap device comprises two main electrodes d and 5 which are made of brass or other low-resistance material having good quenching or non-arcing properties. These electrodes are separated by annular or ring-shaped porcelain insulators 4.

One or both of the main electrodes 4 and 5 are provided with a closely associated auxiliary electrode I of low-breakdown properties but of such high resistivity that any are formed thereon will immediately be transferred to its associated main electrode. In the particular embodiment of my invention which is shown in the drawing, only one of the main electrodes is provided with an auxiliary electrode I, but it will readily be understood that the two main electrodes may be similar to each other.

In the form of my invention which is shown in the drawing, the central portion of the main electrode 4 is provided with a hole or perforation 8, into which is molded, under pressure, a plug 1 of high-resistance material which may consist of a large number of closely spaced silicon-carbide crystals or other conducting particles stuck to gether and to the electrode by a suitable binding material of fairly insulating qualities. The silicon-carbide plug 1 may also be radium-treated, or treated with a radio-active substance, or the radium treatment may be utilized without the utilization of silicon-carbide crystals, the latter being replaced by any substance or ingredient for giving the plug its desiredhigh-resistance electrical conductivity. This high-resistance plug 1 is closely associated with its main gap-electrode 4, so that both elements are spaced from the other main electrode 5 by approximately the same gap or distance 9, although the gap-length or spacing between the high-resistance plug 1 and the other main electrode 5 from which it is spaced is preferably slightly greater than the mainelectrode gap-spacing 9, as shown on the drawing.

It is usually desirable that the height or axial length of the spacer-ring 6 shall be considerably greater than the gap-spacing 9, and to this end one or both of the main electrodes are dished inwardly. In the embodiment shown, the main electrode 4 which carries the silicon-carbide plug I is centrally dished, so as to approach to the distance 9 from the other main electrode 5, which is flat. In the center of this dished portion the hole 8 is punched, and the material surrounding the edges of the hole is punched backwardly, away from the other main electrode 5, so as to leave a rounded annular portion of the main electrode 4, surrounding the plug I, for providing the main gap 9.

One or more of the above-described series-gap devices are utilized in series with one or more lightning-arrester elements as diagrammatically indicated at II, the whole being connected between the electrical circuit or conductor I2 which is to be protected, and the ground l3, the number of serially connected devices depending upon the voltage.

When a voltage is applied to the series-gap device, and increased in magnitude, the material of the plug I will give oil free electrons at a lower average voltage-gradient than the material of the main electrode-portions 4 and 5, and the presence of these electrons affects the breakdown of the gap. It has been found that this effect is most noticeable on the breakdown characteristics of the gap under surge-conditions, resulting in a uniformly low breakdown of the gap under surge conditions. When voltage is first applied to the series-gap device, the plug 1, prior to the breakdown of the gap, assumes substantially the same potential as the main electrode 4 with which it is associated. The rising potential on this electrode causes capacitive chargingcurrent to flow across the gap 8 between the plug I and the other main electrode 5, and it is necessary for this charging current to pass from the main electrode 4 through the interior of the plug 1 to the gap-terminal surface thereof. This passage of current through the plug I may produce high potential-gradients between the conducting particles or crystals, and these potentialgradients liberate electrons which influence the breakdown-voltage of the gap and cause it to be consistently low in comparison to the breakdown-voltage of a gap made altogether with the material of the two main electrodes 4 and I without the plug-insert I.

Once the arc has been formed, there will be a considerable resistance-drop caused by the flow of any arc-current through the high-resistance material of the plug I, and moreover the high resistivity of the arc-terminal surface ii of the plug 1 will cause the terminal of the arc to spread out on this surface, rather than concentrating in a small area thereof, so that any are which is formed on the surface of the plug 1 will immediately transfer to the adjacent surface of the associated electrode 4, this transfer being facilitated by the slight difference between the gap-spacings of the main and auxiliary electrodes. This not only prevents excessive heating of the high-resistance plug I, but it causes the series gap device to retain the same arc-quenching ability which it would have had if the auxiliary plug I had not been utilized.

Comparative tests with my new gap-devices, as compared to previous gap-devices, has shown that none of the gaps, new or old, has an absolutely fixed breakdown-voltage which is the same for all gaps which, so far as can be determined without a breakdown-test, are identical with each other. Like most other physical properties of materials, the breakdown-values of a large number of apparently similar gaps are scattered, some high and some low. With the old gaps, not only is the average breakdown-value higher, but the range between high and low values is greater, than in my new gaps. I have found that my new gaps with radium-treated silicon-carbide plugs have a somewhat less scattered range of surge-breakdown-values, or a more consistently predictable breakdown, for a given gap-spacing, than my new gaps with non-radium-treated silicon-carbide plugs; while the surge-breakdownvalues of the latter are, in turn, enormously less scattered, or more consistent, and also much lower in average value, than the old gaps without any silicon-carbide plugs.

When I refer to an arc-initiating function or operation, I mean to include also a spark-initiating function or operation, without fine discriminations as to whether the initial discharge is a spark or an are.

I claim as my invention:

1. A series-gap device, comprising spaced main electrodes of relatively good-conducting material capable of becoming the terminal of a concentrated arc-discharge and having adequate quenching properties, and arc-initiating means associated with at least one of said main electrodes; said arc-initiating means comprising an auxiliary electrode of relatively poor-conducting material alongside of said main electrode, said relatively poor-conducting material containing a radio-active substance and having such poor conductivity as to be incapable of maintaining an are on its surface in the presence of the main electrode.

2. A series-gap device, comprising spaced main electrodes of relatively good-conducting material capable of becoming the terminal of a concentrated arc-discharge and having adequate quenching properties, and arc-initiating means associated with at least one of said main electrodes; said arc-initiating means comprising an auxiliary electrode of relatively poor-conducting material alongside of said main electrode, said relatively poor-conducting material comprising a small amountof radio-active substance, a binding material of fairly insulating qualities, and a large number of closely spaced conducting particles dispsersed therein.

3. A series-gap device, comprising spaced main electrodes of relatively good-conducting material capable of becoming the terminal of a concentrated arc-discharge and having adequate quenching properties, and arc-initiating means associated with at least one of said main electrodes; said arcinitiating means comprising an auxiliary electrode of relatively poor-conducting material alongside of said main electrode, said relatively poor-conducting material comprising a small amount of radio-active substance, a binding material of fairly insulating qualities, and a large number of closely spaced silicon-carbide particles dispersed therein.

4. A series-gap device, comprising spaced main electrodes of relatively good-conducting material capable of becoming the terminal of a concentrated arc-discharge and having adequate quenching properties, at least one of said main electrodes having a central depression therein, and an arc-initiating substance disposed within said depression, said arc-initiating substance comprising relatively poor-conducting material containing a radio-active substance and having such poor conductivity as to be incapable of maintaining an are on its surface in the presence of the main electrode.

5. A seriesgap device, comprising spaced main electrodes of relatively good-conducting material capable of becoming the terminal of a concentrated arc-discharge and having adequate quenching properties, at least one of said main electrodes having a central depression therein, and an arc-initiating substance disposed within said depression, said arc-initiating substance comprising relatively poor-conducting material comprising a small amount of radio-active substance, a binding material of fairly insulating qualities, and a large number of closely spaced conducting particles dispersed therein.

6. A series-gap device, comprising spaced main electrodes of relatively good-conducting material capable of becoming the terminal of a concentrated arc-discharge and having adequate quenching properties, at least one of said main electrodes having a central depression therein, and an arc-initiating substance disposed within said depression, said arc-initiating substance comprising a small amount of radio-active substance, a binding material of fairly insulating qualities, and a large number of closely spaced silicon-carbide particles dispersed therein.

7. A series-gap device, comprising spaced main electrodes of relatively good-conducting material capable of becoming the terminal of a concentrated arc-discharge and having adequate quenching properties, and arc-initiating means associated with at least one of said main electrodes; said arc-initiating means comprising an auxiliary electrode of relatively poor-conducting material alongside of, and in electrical connection to, said associated main electrode and spaced entirely in noncontacting, discharge-gap relation to the other electrode, said relatively poorconducting material having better discharge initiating qualities than the material of said associated main electrode but having such poor conductivity as to be incapable of maintaining an are on its surface in the presence of said associated main electrode, whereby the are after initiation is transferred to said associated main electrode, and means for conducting current directly to and from the terminal main electrodes during the continuance of said arc.

8. A series-gap device, comprising spaced main electrodes of relatively good-conducting material capable of becoming the terminal of a concentrated arc-discharge and having adequate quenching properties, and arc-initiating means associated with at least one of said main electrodes; said arc-initiating means comprising an auxiliary electrode of relatively poor-conducting material alongside of, and in electrical connection to, said main electrode and spaced entirely in non-contacting, discharge-gap relation to the other electrode, said relatively poor-conducting material having an exposed discharge-gap surface which emits electrons at a lower average voltage-gradient than said associated main electrode but having such poor conductivity as to be incapable of maintaining an are on its surface in the presence of said associated main electrode, whereby the are after initiation is transferred to said associated main electrode, and means for conducting current directly to and from the terminal main electrodes during the continuance of said arc.

9. A series-gap device, comprising spaced main electrodes of relatively good-conducting material capable of becoming the terminal of a concentrated arc-discharge and having adequate quenching properties, and arc-initiating means associated with at least one of said main electrodes; said arc-initiating means comprising an auxiliary electrode of relatively poor-conducting material alongside of, and in electrical connection to, said associated main electrode and spaced entirely in non-contacting, discharge-gap relation to the other electrode, said relatively poor-conducting material comprising a binding material of fairly insulating qualities and a large number of closely spaced conducting particles dispersed therein, whereby the are after initiation is transferred to said associated main electrode, and means for conducting current directly to and from the terminal main electrodes during the continuance of said are.

10. A series-gap device, comprising spaced main electrodes of relatively good-conducting material capable of becoming the terminal of a concentrated arc-discharge and having adequate quenching properties, and arc-initiating means associated with at least one of said main elec trodes; said arc-initiating means comprising an auxiliary electrode of relatively poor-conducting material alongside of, and in electrical connection to, said associated main electrode and spaced entirely in non-contacting, discharge-gap relation to the other electrode, said relatively poor-conducting material comprising a binding material of fairly insulating qualities and a large number of closely spaced silicon-carbide particles dispersed therein, whereby the are after initiation is transferred to said associated main electrode, and means for conducting current directly to and from the terminal main electrodes during the continuance of said are.

11. A series-gap device, comprising spaced main electrodes of relatively good-conducting material capable of becoming the terminal of a concentrated arc-discharge and having adequate quenching properties, at least one of said main electrodes having a central depression therein, and an arc-initiating substance disposed within said depression in electrical-contact relation to the associated main electrode and spaced entirely in non-contacting, discharge-gap relation to the other electrode, said arc-initiating substance comprising relatively poor-conducting material having better dischargednitiating qualities than the material of said associated main electrode but having such poor conductivity as to be incapable of maintaining an arc on its surface in the presence of said associated main electrode. whereby the are after initiation is transferred to said associated main electrode, and means for conducting current directly to and from the terminal main electrodes during the continuance of said arc.

12. A series-gap device, comprising spaced main electrodes of relatively good-conducting material capable of becoming the terminal of a concentrated arc-discharge and having adequate quenching properties, at least one of said main electrodes having a central depression therein, and an arc-initiating substance disposed within said depression in electrical-contact relation to the associated main electrode and spaced entirely in non-contacting, discharge-gap relation to the other electrode, said arc-initiating substance comprising relatively poor-conducting material having an exposed discharge-gap surface which emits electrons at a lower voltage than said associated main electrodebut having such poor conductivity as to be incapable of maintaining an are on its surface in the presence of said associated main electrode, whereby the are after initiation is transferred to said associated main electrode, and means for conducting current directly to and from the terminal main electrodes during the continuance of said are.

13. A series-gap device, comprising spaced main electrodes of relatively good-conducting material capable of becoming the terminal of a concentrated arc-discharge and having adequate quenching properties, at least one of said main electrodes having a central depression therein, and an arc-initiating substance disposed within said depression in electrical-contact relation to the associated main electrode and spaced entirely in non-contacting, discharge-gap relation to the other electrode, said arc-initiating substance comprising a binding material of fairly insulating qualities and a large number of closely spaced conducting particles dispersed therein, whereby the are after initiation is transferred to said associated main electrode, and means for conducting current directly to and from the terminal main electrodes during the continuance of said arc.

14. A series-gap device, comprising spaced main electrodes of relatively good-conducting material capable of becoming the terminal of a concentrated arc-discharge and having adequate quenching properties, at least one of said main electrodes having a central depression therein, and an arc-initiating substance disposed within said depression in electrical-contact relation to the associated main electrode and spaced entirely in non-contacting, discharge-gap relation to the other electrode, said arc-initiating substance comprising a binding material of fairly insulating qualities and a large number of closely spaced silicon-carbide particles dispersed therein, whereby the arc after initiation is transferred to said associated main electrode, and means for conducting current directly to and from the terminal main electrodes during the continuance of said arc.

16. A series-gap device, comprising spaced main electrodes of relatively good-conducting material capable of becoming the terminal of a concentrated arc-discharge and having adequate quenching properties, and arc-initiating means associated with at least one of said main electrodes; said arc-initiating means comprising an auxiliary electrode of relatively poor-conducting material alongside of, and in electrical connection to, said associated main electrode and spaced entirely in non-contacting, discharge-gap relation to the other electrode, the gap-length betweensaid relatively poor-conducting material and said other electrode from which it is spaced being greater than the gap-length between the spaced main electrodes of the device, said relatively poor-conducting material having sufiiciently better discharge-initiating qualities than the material of.

said associated main electrode to cause the arc to be initiated on said relatively poor-conducting material in spite of its relatively greater gaplength, said relatively poor-conducting material having such poor conductivity as to be incapable of maintaining an are on its surface in the presence of said associated main electrode, whereby the are after initiation is transferred to said associated main electrode, and means for conducting current directly to and from the terminal main electrodes during the continuance of said arc.

16. A series-gap device, comprising spaced main electrodes of relatively good-conducting material capable of becoming the terminal of a concentrated arc-discharge and having adequate quenching properties, and arc-initiating means associated with at least one of said main electrodes; said arc-initiating means comprising an auxiliary electrode of relatively poor-conducting material alongside of, and in electrical connection to, said associated main electrode and spaced entirely in non-contacting, discharge-gap relation to the other electrode, the gap-length between said relatively poor-conducting material and said other electrode from which it is spaced being greater than the gap-length between the spaced main electrodes of the device, said relatively poor-conducting material having an exposed discharge-gap surface which emits electrons at a sufficiently lower average voltagegradient than said associated main electrode to cause the arc to be initiated on said relatively poor-conducting material in spite of its relatively greater gap-length, said exposed dischargegap surface of the relatively poor-conducting material having such poor conductivity as to be incapable of maintaining an are on its surface in the presence of said associated main electrode, whereby the are after initiation is transferred to said associated main electrode, and means for conducting current directly to and from the terminal main electrodes during the continuance of said arc.

17. A series-gap device, comprising spaced main electrodes of relatively good-conducting material capable of becoming the terminal of a concentrated arc-discharge and having adequate quenching properties, at least one of said main electrodes having a central depression therein, and an arc-initiating substance disposed within said depression in electrical-contact relation to the associated main electrode and spaced entirely in non-contacting, discharge-gap relation to the other electrode, the gap-length between said arc-initiating substance and said other electrode from which it is spaced being greater than the gap-length between the spaced main electrodes of the device, said arcinitiating substance comprising relatively poorconducting material having sufficiently better discharge initiating qualities than the material of said associated main electrode to cause the arc to be initiated on said relatively poor-conducting material in spite of its relatively greater gap-length, said relatively poor-conducting material having such poor conductivity as to be incapable of maintaining an are on its surface in the presence of said associated main electrode, whereby the are after initiation is transferred to said associated main electrode, and means for conducting current directly to and from the terminal main electrodes during the continuance of said arc.

18. A series-gap device, comprising spaced main electrodes of relatively good-conducting material capable of becoming the terminal of a concentrated arc-discharge and having adequate quenching properties, at least one of said main electrodes having a central depression therein, and an arc-initiating substance disposed within said depression in electrical-contact relation to the associated main electrode and spaced entirely in non-contacting, discharge-gap relation to the other electrode, the gap-length between said arc-initiating substance and said other electrode from which it is spaced being greater than the gap-length between the spaced main electrodes of the device, said arc-initiating substance comprising relatively poor-conducting material having an exposed discharge-gap surface which emits electrons at a sufficiently lower average voltage-gradient than said associated main electrode to cause the arc to be initiated on said relatively poor-conducting material in spite of its relatively greater gap-length, said exposed discharge-gap surface of the relatively poor-conducting material having such poor conductivity as to be incapable of maintaining an are on its surface in the presence of said associated main electrode, whereby the are after initiation is transferred to said associated main electrode, and means for conducting current directly to and from the terminal main electrodes during the continuance of said are.

19. A series-gap device, comprising a spacerring, and a pair of spaced main electrodes disposed one on either side of said spacer-ring, said main electrodes being of relatively good-conducting material capable of becoming the terminal of a concentrated arc-discharge and having adequate quenching properties, at least one of said main electrodes having a central dished portion approaching the other main electrode and having a central depression in said dished portion, and an arc-initiating substance disposed within said depression in electrical-contact relation to the associated main electrode and spaced entirely in non-contacting, discharge-gap relation to the other electrode, said arc-initiating substance comprising relatively poor-conducting material having better discharge-initiating qualities than the material of said associated main electrode but having such poor conductivity as to be incapable of maintaining an are on its surface in the presence of said associated main electrode, whereby the arc after initiation is transferred to said associated main electrode, and means for conducting current directly to and from the terminal main electrodes during the continuance of said arc.

20. A series-gap device, comprising a spacerring, and a pair of spaced main electrodes disposed one on either side of said spacer-ring, said main electrodes being of relatively good-conducting material capable of becoming the terminal of a concentrated arc-discharge and having adequate quenching properties, at least one of said main electrodes having a central dished portion approaching the other main electrode and having a central depression in said dished portion, and an arc-initiating substance disposed within said depression in electrical-contact relation to the associated main electrode and spaced entirely in non-contacting, discharge-gap relation to the other electrode, said arc-initiating substance comprising relatively poor-conducting material having an exposed discharge-gap surface which emits electrons at a lower voltage than said associated main electrode but having such poor conductivity as to be incapable of maintaining an arc on its surface in the presence of said associated main electrode, whereby the are after initiation is transferred to said associated main electrode, and means for conducting current directly to and from the terminal main electrodes during the continuance of said are.

FREDERICK B. JOHNSON. 

